Field of the Invention
The present invention relates to a “multipoint” fuel injection device for an annular combustion chamber of a turbine engine such as an airplane turboprop or turbojet.
Description of the Related Art
In known manner, a turbine engine has an annular combustion chamber arranged at the outlet from a high-pressure compressor and provided with a plurality of fuel injection devices that are regularly distributed circumferentially at the inlet of the combustion chamber. A “multipoint” injection device has a Venturi with a pilot injector mounted therein centered on the axis of the Venturi and continuously fed with fuel by a pilot circuit, and a second Venturi that is coaxial around the first. The second Venturi has an annular chamber at its upstream end with an annular ring mounted therein that is fed with fuel by a fuel circuit. The ring has fuel injection orifices formed in its front face that faces downstream. These orifices open out downstream into orifices in a front wall of the annular chamber that themselves open out into the combustion chamber.
The pilot circuit supplies a continuous flow of fuel that is optimized for low speeds, and the multipoint circuit supplies an intermittent flow of fuel that is optimized for high speeds.
Nevertheless, intermittent use of the multipoint circuit has the major drawbacks resulting from the effect of high temperatures due to radiation from the flame in the combustion chamber of giving rise to stagnant fuel inside the multipoint circuit clogging or coking when the multipoint circuit is not in operation. These phenomena can lead to coke forming in the fuel injection orifices of the multipoint circuit thereby impeding or reducing the spraying of fuel by the multipoint circuit and thus impeding or reducing the operation of the combustion chamber.
In order to mitigate that drawback, document EP 2 026 002 in the name of the Applicant proposes using a fuel pilot circuit for cooling the multipoint circuit and reducing the formation of coke therein by means of two annular channels that are formed in the annular chamber radially on the outside and on the inside of the annular ring, these two channels having their outlets connected to the pilot injector. In document FR 09/04906, the Applicant has also proposed arranging thermal insulation means between the front face of the chamber and the front wall of the annular chamber. In another document FR 09/04907, the Applicant has proposed cooling the front face of the ring by diverting a fraction of the fuel from the inner or outer annular channels and causing it to flow between the front face of the annular ring and the front wall of the annular chamber.
Although those techniques reduce the coking of fuel in the vicinity of the orifices in the ring, that reduction is nevertheless not sufficient to guarantee good operation of the multipoint circuit.
Securing the annular ring inside the annular chamber and ensuring good sealing between the multipoint circuit and the pilot circuit make it necessary to provide welding or brazing between the front face of the ring and the front wall of the chamber. Thus, a zone of contact exists between the front face of the ring and the front wall of the chamber, thereby leading to good conduction of heat flux from the combustion flame towards the orifices in the ring and thus running the risk of forming coke when the multipoint circuit is not in operation.